Changes in the reflected and transmitted color of esthetic brackets after thermal cycling

The objective of this study was to determine the changes in the reflected and transmitted color and the color parameters of esthetic brackets after thermal cycling.

Four brands of plastic and 4 brands of ceramic brackets were investigated. Reflected color of the labial side of bracket was measured according to the Commission Internationale de l'Eclairage (CIE) LAB color scale before and after thermal cycling for 5000 cycles. Transmitted color was measured with the same measurement protocol. Color change was calculated with the equation: DeltaE*(ab) = [(DeltaL*)(2)+ (Deltaa*)(2)+ (Deltab*)(2)](1/2). Changes in color parameters such as lightness (CIE L*), chroma (C*(ab)), CIE a* and b* values were calculated as the value after thermal cycling minus the value before thermal cycling. One-way analyses of variance were performed for the changes in color and color parameters by the brand of bracket (alpha = 0.05), and the Tukey multiple comparison test was performed.

Changes in the reflected and transmitted color and the color parameters were influenced by the brand of bracket (P <0.05). Reflected color change was 1.4 to 6.4 DeltaE*(ab) units, and transmitted color change was 1.0 to 2.8 DeltaE*(ab) units. Kind of material (plastic or ceramic) and crystal structure of ceramic brackets did not influence color stability, but color stability was mainly brand-dependent.

Reflected color changes of 3 of 8 brands were in the clinically perceptible range (DeltaE*(ab) > 3.7). Therefore, color stability of esthetic brackets should be enhanced for long-term esthetic performance of these brackets.